The innovative engine now propelling NASA's Deep Space 1
spacecraft toward its ambitious September encounter with Comet
Borrelly just won't give up, having now run for more than
10,000 hours -- 50 times beyond its originally required
lifetime.

A working replica of the Deep Space 1 ion engine has
logged in even more hours at NASA's Jet Propulsion Laboratory,
Pasadena, Calif., where the mission is managed.

The spacecraft's engine was only required to complete 200
hours of operation in flight to prove itself a success. On
March 21, it passed the 10,000-hour mark. It's expected to
pass 14,000 hours by the end of its extended mission to Comet
Borrelly.

The ion engine works by first removing an electron from
the gas xenon, then using a pair of electrically charged grids
to shoot the ionized gas out at more than 35,000 meters per
second (78,000 miles per hour). The engine is one of a dozen
important new technologies that the successful Deep Space 1
mission officially finished testing in 1999. Now that Deep
Space 1 has been approved for a risky extended mission to
Comet Borrelly, the long-lived ion engine will take the
spacecraft near the comet. Similar ion engines may be used on
future space missions, particularly missions to comets and
asteroids where the ion engine's high fuel economy is
important for precise navigation to the small bodies.

"The ground-based xenon ion engine has run for about
15,500 hours of testing time since the test began in early
October 1998," said Dr. John Anderson of JPL, the ion engine
test lead engineer. "That's more than 150 percent of the time
it was designed to last."

"The results from Deep Space 1 and testing on the ground
show that ion engines can be terrifically effective," said
JPL's Dr. Marc Rayman, the project manager of Deep Space 1.
"Now I'm looking forward to future spacecraft that use ion
engines surpassing Deep Space 1's record as they undertake
still more exciting missions."

Engineers partly attribute the secrets to the ion
engine's long life to a slight increase in the flow of xenon
through the engine early in the testing phase. "This reduced
the amount of wear on the engine, and yet didn't significantly
affect the engine's efficiency," said Dr. John Brophy, manger
of NASA's Solar Electric Propulsion Technology Applications
Readiness project.

Anderson began testing the ground-based ion engine when
it was shipped to JPL from Hughes, which is now part of
Boeing, in 1998. "We'd like to test it until the end of its
life. Then we'll see how to make these engines last even
longer," he said. He had also tested an earlier version of
the ion engine, beginning in 1996.

The ion engine is tested for about 75 percent of the time
over the two and a half years of the test, Anderson said, with
other time spent on running diagnostic tests, and defrosting
the xenon propellant that had become frozen in the vacuum
system. At first, the engine was run at just more than half of
its capacity, about 1.5 kilowatts, and then upped to full
capacity, 2.3 kilowatts. The next phase of the test will be to
run the engine at its lowest thrust level to demonstrate the
engine's ability to run at low power near the end of its life,
Anderson said.

Deep Space 1 has operated its ion engine between 520
watts and 1.9 kilowatts, in part depending upon the
spacecraft's distance from the Sun during its flight in space.
Deep Space 1's ion engine now also helps the spacecraft
maintain its orientation relative to the stars, so it remains
on for 99 percent of the time.

Deep Space 1 was launched in October 1998 as part of
NASA's New Millennium Program, which is managed by JPL for
NASA's Office of Space Science, Washington, D.C. The
California Institute of Technology in Pasadena manages JPL for
NASA.